[Greenbuilding] Exhaust Only Passive Inlet Ventilation

[Nick Pine]

John Straube <jfstraub at civmail.uwaterloo.ca> writes:

> In the past I have used, with resistance from code officials and 
> designers, exhaust fans in bath rooms (operating continuously or 20 
> minutes of each hour)

It would be nice to ventilate only as needed, to save energy... 30 cfm 
is about 24hx30cfmx10K = 7.2 million Btu (2100 kWh) per year in a 10K DD 
(F) climate, no? Like 72 gallons of oil or therms of gas or a little 
more solar heat collection and storage and distribution capacity.

>and air inlets (from Panasonic or Aldes) in each room in numerous 
>houses (one storey houses so that stack effect does not cause air to 
>flow in on the lower floor and out the top floor vents) and a few wood 
>frame apartments (with airtight  separations between units) and one 
>muliti-storey concrete building (my own, with tight floor 
>seperation)...

Mmultifamily situations seem more complex in that we want fresh air in 
every apartment, but we don't want mix air between apartments. Ever 
tried "Shurcliff's lung" in the form of a small periodically-reversing 
fan in an airtight partition between 2 parts of a house that runs when 
fresh air is needed, turning all the external cracks and crevices in 
each half into tiny efficient bidirectional heat exchangers? Or 
Scandinavian breathing walls with a stack-effect chimney and a motorized 
damper to adjust the flow?

> The RH control does not work, although has been tried by many. In the 
> winter, ventilation is very important to lower indoor RH, and people 
> naturally try to button up their homes and close windows for comfort. 
> Setting the humidistat at 60% will mean no ventilation occurs in a 
> cold climate until it there is so much moisture that water is running 
> down the windows and rotting walls and roofs. You could set it at a 
> safer 35% in Ottawa or 40% in Boston, but then it would over ventilate 
> during the spring. Then in nice weather when people leave the windows 
> open and ventilation is not needed the fan would run like made trying 
> to het the RH down to 60% by bringing in lots of 65% air :) Someone 
> would have to know how to adjust it.

I was thinking more about how to provide just enough fresh air than how 
to avoid condensation. IIRC, Honeywall makes a humidifier control that 
lowers the indoor RH when it's cold outdoors to avoid condensation. It 
has a knob for one-time occupant tweaking if condensation is ever seen, 
but it does not require an outdoor temp sensor, just a furnace duct 
sensor. I wonder how they do that. Sensing the furnace run time, which 
would increase in cold weather?

> Hence, other than fixed ventilation, the two controls that seem to 
> work are timing controls and CO2 controls. The latter is the best.

And expensive, at $500 and up, it seems.

>Occupancy controls can be used to boost base level ventilations but not 
>in exclusion because there are pollutants in a space that are not 
>occupancy related that need some ventilation.

So we need some constant small flow of fresh air, and more when the 
house is occupied, and it may be more or less airtight, and people 
create humidity (2 gallons per day for an average family of 4, by 
Andersen's estimate), and the outdoor temp and RH and windspeed vary...

Perhaps a smart ventilation controller (eg an $85 Norhtec PC and 2 $44 
Aagelectronica 1-wire temp/RH sensors) can estimate how much water 
people evaporate and evaporate more inside a house (with some geothermal 
heat from a soaker hose on a basement floor? :-) if needed to raise the 
RH to 40% in wintertime, and estimate the natural air leakage of the 
house based on the amount of water required to do that, and run an 
exhaust fan as needed to maintain a total 15 cfm per occupant when the 
house is occupied.

Buildings and building materials can store fresh air and moisture, so it 
might ventilate when outdoor air is dryer if the house needs 
dehumidification and when outdoor air is warmer if the house needs heat. 
It might also run $80 indoor and outdoor window ACs, if dehum is needed 
but fresh air isn't.

Nick